Ethanol is an industrially important material and finds large consumptions especially in food processing and medicinal preparations and as a fuel additive. Commercialized processes for the preparation of ethanol include fermentation of sugar, various types of starch or other raw materials obtained from plants.
In parallel with the plant-based processes, extensive studies have been made to produce ethanol from coal and natural gas, now known as the most potent petroleum substitute carbon sources. As a result, several processes have been proposed. In European Patent Publication No. 0 172 431A2, assigned to the Dow Chemical Company, and U.S. Pat. No. 4,122,110, assigned to Institute Francais du Petrole, catalytic processes for producing alcohols directly from synthesis gas are disclosed. However, these processes require rather severe reaction conditions such as high pressure, and their product selectivity is undesirably low. The resulting alcoholic products from these processes are said to contain 30-60% methanol and a mixture of higher alcohols.
As another approach, U.K. Patent Publication No. 2 053 915 A, assigned to British Petroleum, describes a reaction comprising the steps of forming methanol from synthesis gas by a commercially established catalytic process and catalytically reacting or homologating the resulting methanol with synthesis gas to form ethanol. In the preferred embodiment of the catalytic reaction, selectivity to ethanol is said to be about 80% based on the amount of methanol used. However, many problems have been encountered in the commercialization of the process due to such problems as the severe reaction conditions required and the presence of considerable amounts of by-products.
As still another approach, attempts have been made to esterify acetic acid to form methyl or ethyl acetate which is then hydrogenated to form ethanol. For example, International Publication No. WO 83/034409, asigned to Davy McKee Ltd. and U.K. Patent Publication No. 2 162 172 A disclose processes for preparing ethanol, which comprise forming acetic acid by a liquid phase carbonylation of methanol, esterifying the resulting acetic acid to form methyl acetate followed by the hydrogenation thereof to form ethanol. See also B. Juran and R. V. Porcelli of Halcon SD Group, Hydrocarbon Processing, 85 (Oct. 1985). However, these processes for the preparation of ethanol by hydrogenating methyl acetate, including the Halcon process, have experienced serious problems including a high production cost of the methyl acetate.
As a still further approach, BASF and Humphreys & Glassgow have reported a simpler conversion process. Specifically, in European Patent Nos. 56 488 and 100 406, there is proposed a method of directly converting acetic acid into ethanol without involving an esterification step. Despite the absence of the esterification step, however, there still exist various problems: for instance, the ethanol so produced should be separated from water; and since hydrogenation is carried out at a high reaction pressure, e.g., 4000 psi, the equipment cost may also be very high.